arm64: ASLR: Don't randomise text when randomise_va_space == 0

When user asks to turn off ASLR by writing "0" to
/proc/sys/kernel/randomize_va_space there should not be
any randomization to mmap base, stack, VDSO, libs, text and heap

Currently arm64 violates this behavior by randomising text.
Fix this by defining a constant ELF_ET_DYN_BASE. The randomisation of
mm->mmap_base is done by setup_new_exec -> arch_pick_mmap_layout ->
mmap_base -> mmap_rnd.

Signed-off-by: Arun Chandran <achandran@mvista.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

arch/arm64/kernel/process.c

@@ -378,8 +378,3 @@ unsigned long arch_randomize_brk(struct mm_struct *mm)
 {
 	return randomize_base(mm->brk);
 }
-
-unsigned long randomize_et_dyn(unsigned long base)
-{
-	return randomize_base(base);
-}